I have a desktop which uses only an AR8161 Ethernet card to connect to the Internet but it does not work whenever I go into Ubuntu. Is it a driver issue or some configuration issue? How can I go about resolving it?
Your device is covered by the driver alx which is not present until later versions of Ubuntu 12.10 and 13.04. You could download the driver and all its prerequisites on another computer (a very complex and tedious process) and transfer them on a USB drive; you could install a later 3.8 kernel or you could re-install 13.04.
If you decide on a later kernel, be sure to download and install linux-image as well as linux-image-extra.